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Abstract

This paper presents experimental results from a pulsed quantum cascade laser based cavity ringdown spectrometer used as a high-throughput detection system. The results were obtained from an optical cavity with 99.8% input and output coupling mirrors that was rapidly swept (0.2s to 7s sweep times) between 1582.25 cm−1 (6.3201μm) and 1697.00 cm−1 (5.8928μm). The spectrometer was able to monitor gas species over the pressure range 585 torr to 1μtorr, and the analysis involves a new digital data processing system that optimises the processing speed and minimises the data storage requirements. In this approach we show that is it not necessary to make direct measurements of the ringdown time of the cavity to obtain the system dynamics. Furthermore, we show that correct data processing is crucial for the ultimate implementation of a wideband IR spectrometer that covers a range similar to that of commercial Fourier transform infrared instruments.

Measurement of ≈ 1m room air at 1 atmosphere (at 7500ft. elevation above sea level) using the QCL (blue) compared to the HITRAN data base (red). The QCL data has been normalised by the laser intensity at each wavelength.